1. Field of the Invention
The present invention relates to an image analysis method for automatically identifying an object in a background by generating a description of the gray level space of an image of the object and the background. Object identification is enhanced by determining the interior points of the object, thereby further characterizing the object by color, texture and pattern.
2. Description of the Related Art
The ability to access interior points of a region when its contour is given is a classic problem in image processing. Previous solutions to this problem have been described by L. W. Chang and K. L. Leu in an article entitled "A Fast Algorithm for the Restoration of Images Based on Chain Codes Description and Its Application", Computer Vision, Graphics, and Image Processing, 50, 296-307 (1990). One algorithm described, connectivity filling, requires that every pixel in the object be interrogated. Since the number of pixels within an object is greater than the number of pixels which comprise the perimeter of the object, such a technique is relatively slow. Another method described is parity checking, which is based on the fact that the intersection of a straight line with the contour regions of an object delineates an even number of points on the perimeter of the object. Designation of the interior points is determined by an arbitrary filling rule, where all points between each odd point and the next even point on the contour in each line of the image are designated as interior points. Such a parity checking algorithm will not work with objects of complex shape.
In the same article cited above, Chang and Leu propose an enhanced parity checking algorithm which relies on characterizing the perimeter points into one of four categories, based on direction code values. Characterizing the points leads to the creation of a new buffer of perimeter points, wherein some points have been duplicated and others eliminated. By applying the parity checking algorithm to the newly created buffer, interior points of objects with complex shapes may be identified. However, the enhanced algorithm presented by Chang and Leu is an indirect method for solving the problem of interior point determination, requiring an excessive number of steps.
Japanese Patent Publication Number 62-60069 to Hitachi Electronic Engineering Co., Ltd., published on Dec. 14, 1987, discloses a colony screening device which distinguishes colonies based on color. Colonies are identified by pattern recognition using a predetermined threshold, and a small number of points in the center of a colony are arbitrarily selected. This publication does not disclose a method for determining all the interior points of an object. Limiting the area of determination introduces possibilities of error into any attempt at object identification.
U.S. Pat. No. 4,453,266 to Bacus discloses a method for measuring the optical density of a cell using the sum of the gray level values within the closed boundaries of the cell. Bacus does not contemplate determining all of the interior points of an object of an unknown or arbitrary shape using an automatic thresholding technique.
None of the references discussed above discloses a method for identifying and characterizing, by color, a valid object having at least one predetermined attribute value in a background using automatically calculated thresholds by determining the interior points of the object. Moreover, none of the references discussed above discloses a method for identifying and characterizing, by color, a valid object in a varying background.